Apparatus for molding and perforating a FRP sheet

ABSTRACT

Apparatus for making a soundproof lining for a gas pipe, in particular for a turbojet fan jet, of the type including a multiplicity of thin, perforated panels juxtaposed by tiling, as well as an intermediate layer between the wall of the pipe and each of said panels to delimit with said perforated panel a multiplicity of resonant acoustical cavities in which the acoustical vents consist of the ports in the perforated panel. According to the invention, in order to make the tubular vents, each perforated panel has a short, tubular sleeve at right angles to each port and located on its face opposite the wall of the pipe.

This is a division of application Ser. No. 342,733, filed Jan. 26, 1982,now U.S. Pat. No. 4,449,607.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention concerns a soundproof lining for a gas pipe. Italso concerns tools for fabricating elements of this lining.

The invention's lining, because of its thinness, lightness, good impactresistance and ease of installation, is particularly suitable forsoundproofing the upstream and downstream housings of a turbojet fan.Generally speaking, it can be used advantageously whenever it isnecessary to reduce the noise level produced in a large-diameter streamby a gas flow with a relatively low temperature.

2. Description of the Prior Art

The lining of the invention is of the type consisting of thejuxtaposition of composite soundproofing panels within which areresonant cavities which communicate with the gas flow by a multiplicityof vents. Such composite panels are already known, in particular throughthe French Pat. No. 2 201 010. They include two sheets facing oneanother, one of which, in contact with the gas flow, is perforated.These two sheets are braced by a corrugated sheet, the corrugations ofwhich delimit the resonant cavities. The three sheets are of metal andare rigidly assembled by brazing. Such composite panels must haveprecise radii of curvature since their rigidity makes it impossible tocompensate for size defects by deformation during assembly. Thisrigidity is even more bothersome when the gas flow stream islarge-sectioned. The wall of the stream itself has curve defects. Theproblem can be solved by interposing a mattress of a flexible and porousmaterial, as has already been proposed in the French Pat. No. 2 396 868.But this solution is only suitable for relatively small-sectionedstreams. Otherwise the lining becomes too cumbersome and heavy.

SUMMARY OF THE INVENTION

The soundproof lining of the invention is free from these drawbacks. Itselements are light and easy to assemble. It is quickly fabricated. Itincludes both a multiplicity of rigid and thin perforated panelsjuxtaposed by shingling (that is, one of the edges of one panel coversthe edge of an adjacent panel) and, in addition, an intermediate layershaped so as to delimit, together with said perforated panel, amultiplicity of resonant acoustical cavities in which the acousticalvents consist of the ports in the perforated panel. Each perforatedpanel is provided with means for direct attachment to the wall formingan interval between it and this perforated panel, and the intermediatelayer is an intermediate ductile panel housed and held in this interval.

The relative flexibility of the perforated panels (due to theirthinness) and the ductility of the intermediate panels make it possiblefor the lining to be adapted upon assembly to the conformation defectsof the jet stream's wall.

But the lining according to the invention has other characteristics andadvantages as well. It is known that the resonance frequencies of acavity depend on its volume and the acoustical resistance of its vent orvents. It is known that the acoustical resistance of a vent can beincreased by giving it a tubular shape. The more this acousticalresistance contributes to the cavity's acoustical impedance, the moreits resonance frequencies expand and the more the cavity becomes capableof absorbing noise in frequency bands that are appreciably differentfrom its nominal resonance frequencies. To achieve this advantageouseffect despite the thinness of the perforated panels of the invention,each of these panels has, at right angles to each of its ports and onits face facing the wall, a short tubular sleeve, the bore of whichextends said port to form a tubular vent.

Advantageously, each perforated panel consists of a thin sheet of moldedpolymer resin reinforced with mineral or organic fibers. Not only is itthus light, relatively rigid, and has good elongation characteristicsenabling it to take major deformations under impact, but, in addition,the tubular sleeves may be molded together with the sheet. Theirattachment to this sheet is all the more secure since, according to theinvention, the reinforcement fibers penetrate said sleeves.

Other advantageous features of the invention involve the intermediatepanel housed between the wall and each perforated panel. In order thatsuch an intermediate panel will be both relatively flexible and capableof forming, with the perforated panel, resonant cavities tight againstone another, the invention provides for the following:

1. The intermediate panel consists of a thin sheet of polymer resin(preferably elastomer) held against the wall of the stream by theperforated panel and has ribs the edges of which are held against thisperforated panel and which delimit the resonant cavities.

2. In order to prevent the perforated panel from crushing the edges ofthe ribs (crushing would damage the tightness between the adjacentcavities), these rib edges are flanged. This arrangement becomesparticularly advantageous when the lining is in a turbojet fan stream,since the ductility of these flanged edges appreciably increases themechanicalenergy absorption capacity of said lining because, unlike theknown structures, the intermediate ribbed panel is not closely attachedto the perforated panel and can freely follow deformations and resumeits initial shape. The perforated panel much better resists repeatedhammerings by grit and gravel.

3. In order to facilitate application of the intermediate panel againstthe wall, this intermediate panel has short ribs on the face oppositesaid wall.

4. The intermediate panel is mounted with prestress, which consequentlyachieves a certain damping of the perforated panel against acousticalvibrations.

The tools for making the perforated panels include a fixed mold part anda movable mold part, both to be inserted between the plates of a press,and forming a molding cast. A multiplicity of pins are intended to formthe ports of the panel during molding, when the mold is completelyclosed, each of these pins passes through one of the mold parts though,a pin passage, crosses through the cast, and penetrates the other moldpart through another pin passage.

Recesses are made at the outlet into the cast of the pin passages of oneof the parts of the mold to form molding casts for the tubular sleeves.The pins are made of steel and are covered with a layer of oxide whichfavors the attachment of an unmolding agent.

BRIEF DESCRIPTION OF THE DRAWINGS

Various other objects, features and attendant advantages of the presentinvention will be more fully appreciated as the same becomes betterunderstood from the following detailed description when considered inconnection with the accompanying drawings in which like referencecharacters designate like or corresponding parts throughout the severalviews, and wherein:

FIG. 1 is a large-scale partial cross section, taken in the plane 1--1of FIG. 2, of a fan jet equipped with a lining according to theinvention;

FIG. 2 is a partial cross section on the same scale, taken in the plane2--2 of FIG. 1, of said fan jet;

FIG. 3 is a partial section of the mold intended for making theperforated panels of said lining;

FIG. 4 is an enlarged detail of FIG. 3; and

FIG. 5 is a partial cross section analogous to FIG. 1 and showing avariant of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The lining of the invention is intended to soundproof the wall 10 of afan jet, as seen in FIGS. 1 and 2. It includes a multiplicity of thinperforated panels 20 (20A, 20B, etc.) attached to the wall 10 at adistance from the wall 10, as well as a multiplicity of ribbed ductilepanels 30 (a single ductile panel 30A being shown), each of which ishoused and held in the space existing between the wall 10 and aperforated panel 20.

FIG. 1 only shows the perforated panel 20A and the left edge of theadjacent panel 20B. This edge of 20B is engaged upon the right edge of20A so that a continuous perforated wall is formed by such shingling ofthe panels 20.

The parts for attaching each panel 20 to the wall 10 includecountersunkhead bolts 11 (equipped with nuts 12 and lock washers 13),braces 14 and bolt-head hole washers 15. Each of the latter includes aflange 151 which rests on the panel 20 and a body 152 which ispositioned in a centering hole in the associated brace 14. The washers15 and the braces 14 are preferably glued to the panels 20. The latteris thus held rigidly at a distance from the wall 10.

The bolts 11 placed in a single jet section are in reality spacedfarther from one another than is shown in FIG. 1. The two bolts in thisFigure are arbitrarily shown closer together to illustrate the case inwhich a bolt (bolt 11 on the left) assures attachment of an area of asingle panel 20 (here 20A) and the case in which a single bolt (bolt 11on the right) assures simultaneous attachment of the edges of two panels20 (here, 20A and 20B).

FIG. 5 shows a variant, according to the invention, of the method forattaching each panel 20 to the wall 10 while keeping each panel rigidlyat a distance from the wall. The attachment pieces, in addition to thebolts 11, nuts 12, and stop washers 13 described above and shown inFIGS. 1 and 2, also include braces 14a, first caps 15a forming holes forthe bolt heads and second caps 15b. In a preferred embodiment, thebraces 14a are molded from a composite material, and theirpolymerization is performed on the spot at the same time as thepolymerization of the panel 20 itself. The caps 15a and 15b are metal,and the first caps 15a are put in place on the panel 20 beforepolymerization, while the second caps 15b are encased in the braces 14aat the time of assembly.

Like the other ribbed panels 30, the panel 30A housed between the sleevejoint 10 and the perforated panel 20A includes a plate-shaped core 31, amultiplicity of support ribs 32 extending toward the perforated panel20A, and a, multiplicity of support ribs 33 extending toward the wall10. Holes such as 34 allow the passage of the braces 14. The latter areequipped with a flange 141 which opposes the movement of the plate 31towards the wall 10. The ribs 33 are very short, as their sole functionis to assure free contact between the wall 10 and the panels 30.

It will be noted that the panel 20A, like the other panels 20 in thesame jet section, includes a flanged upstream edge 22 in order toprotect the panels 30.

The cores 31, the ribs 32 and the panels 20 thus delimit an annularsuccession of cavities which may be divided by ribs in the panels 30which are oriented according to axial planes in the jet stream, andwhich are not shown. Each of these cavities communicates with the jetstream (arrow in FIG. 2) through a multiplicity of small ports 23constituting acoustical vents.

The panels 20, which must be both thin and rigid, are made, for example,of an epoxy resin reinforced with fiberglass (stacking ofpre-impregnated mats).

The ribbed panels 30, which must not be damaged by the tighteningrequired to assemble them, are made of an elastomerpolymer mixture suchas ABS (acrylonitrile-butadiene-styrene).

Other provisions which characterize the lining in FIGS. 1 and 2 arediscussed below. The first consists of the presence, at right angles toeach perforation 23, of a short sleeve 24 placed on the face of eachpanel 20 facing the ribbed panel 30 and the wall 10, the port of whichis an extension of the perforation 23. The second of these provisionsconsists of the fact that the edges 35 of the ribs 32 in contact withthe corresponding panel 20 are flanged edges. It will be noted that theribbed panels 30 are held in place solely by the braces 14, withoutattachment of the panels 30 to the panels 20, nor to the wall 10. Itwill also be seen in FIGS. 1 and 2 that the sleeves 24 are reinforced byfiber ends of the fiberglass reinforcement. It will later be describedhow this result is achieved.

Below, by way of example, are some characteristic sizes in millimetersfor an acoustical lining of a fan housing with a diameter of about 1700mm.

1. Thickness of the perforated panels 20 is 1.5 to 1.9;

2. Thickness of the cores 31 of the ribbed panels 30 is 0.7 to 1;

3. Height of the ribs 32 is 6.5 to 7;

4. Length of the vents 23 is 2 to 5, depending on the acousticalfrequencies to be absorbed.

It can thus be seen that, given the nature of the materials used and thevalues of the thicknesses utilized, the lining according to theinvention is extremely light. It is also provided with an excellentmechanical and acoustical damping factor.

The molding tools according to the invention for making the perforatedpanels 20 of FIGS. 1 and 2 will now be described with reference to FIGS.3 and 4. These tools are intended to be placed between the plates of aheated press, not shown. Generally speaking, no mention will be made ofthe parts or pieces (temperature probes, center punches, gaskets, etc.)whose description would contribute nothing towards understanding theoperation of the tools. For delimiting the molding cast, the toolsinclude a fixed mold part 50 and a movable mold part 60.

The fixed part 50 consists of an assembly of a cooling plate and amolding form. The cooling plate includes from bottom to top a plate 51in which there is a laminar watercirculation cavity 52 as well as afoundation plate 53. The molding form (or die) 54 rests on thefoundation plate 53, and the upper face 55 of the form 54 delimits thelower wall of the molding cast. These elements are assembled by means ofscrews 57.

The movable part 60 includes from bottom to top a molding counterform(or stamp)61 delimiting by its face 62 the upper wall of the moldingcast, a pin support plate 63, and a cooling plate including a plate 64in the upper surface of which is a laminar watercirculation cavity 65,as well as a closing counterplate 66 The pin support plate 63, the plate64 and the counterplate 66 are assembled by means of screws 67.

The ports for passage of the washer bodies 152 (FIGS. 1 and 2) are madeby means of shanks 70 forcibly fitted into bores in the form 54 andwhich can slide in bores in the counterform 61.

To make the vents 23 (FIG. 1 and 2), there are tools including a numberof pins 80, the shanks 81 of which pass through the pin support plate 63and the counterform 61 through bores made for this purpose. These pinsare suspended by their heads 82 at the upper face of the plate 63. Theheads 82 are housed in a recess 68 in the lower face of the plate 64.The thickness of this recess is just sufficient to house them withoutpinching them.

The tools also include small columns 90 sunk into the closingcounterplate 66 and sliding in bores 611 in the counterform 61.Compression springs 91 inserted around these small columns push theplates 63, 64 and 66 away from the counterform 61 when not pressed in bythe press. The small columns 90 have feet 92 with a diameter greaterthan that of their body. These feet slide in recesses 612 in thecounterform 61. They limit the upward course of the small columns. Thiscourse and the length of the pins 80 are such that the ends of the pinsare engaged (when the unit is compressed) in bores of the form 54, andsaid ends do not leave the cast face of the counterform 61 when thesprings 90 retract to the maximum the plates 63, 64 and 66 from thecounterform 61.

According to the invention, shallow recesses 69 are made in the lowerwall 55 at the mouth of each pin bore; they constitute the molding castsfor the sleeves 24 (FIG. 1 and 2). The bodies 81 of the (steel) pins arepretreated so as to be oxidized on the surface. The oxide layer thuscreated favors adherence of an unmolding agent thereon, the agentintended to allow extraction of the pins after polymerization of theresin.

The equipment includes in addition four auxiliary jacks (not shown)which are installed between the plates 51 and 66 in order to allowseparation of the two parts of the mold after polymerization.

The primary phases of the process for making a perforated panel are asfollows. Prior to their use, the pins 80 have undergone a thermaloxidation treatment in an atmosphere of humid argon (500° C. for fourhours) intended to form the adherence layer mentioned above.

1. Preparation of the Equipment

After cleaning, the casting faces of the mold and the pins are coveredby aerosol spray with a silicone unmolding agent. The unmolding layersare then set by heating for one hour at 150° C.

The open mold is placed on the lower plate of a press. The two castfaces are kept at a steady temperature of approximately 135° C. by, forexample, jets of hot air.

2. Preparation and placement of the roughcast

The roughcast includes a stack of precut layers of preimpregnated mat(glass felt with short fibers plus epoxy resin). On either side of thestack is placed a layer of silicone glass cloth intended to give thepanel the desired surface condition. Against the face of the roughcastto be placed alongside the upper wall of the cast (pin 80 penetrationface) is placed a delaminating cloth separated from the roughcast by apolyamide sealant film. The film is intended to prevent sweating of theresin around the pins during pressing and heating. The roughcast is putin place and centered on the lower part 50 of the mold.

3. Closing the mold and molding

The mold is closed in two steps. When the movable part 60 is appliedagainst the fixed part 50, the springs 91 (by means of the plates 66 and64) hold the support plate 63 away from the counterform 61. The pins 80do not yet protrude from the face 62. It is only when the counterform 61is applied by the press against the form 54 that the springs 91 give wayunder the pressure of the press, and the pins 80 penetrate the form 54,passing through the cast. The fibers are not broken by the penetrationof the pins but only pushed aside. They are distributed on either sideof the port and expand into the chambers 69 to form reinforcements forthe sleeves 24 (FIG. 1 and 2), assuring continuity for the transmissionof stress and guaranteeing good stress resistance in the panel. Theheating plates of the press maintain their pressure for 45 minutes, forexample, and the temperature of the entire mold is 135° C.

4. Unmolding

A current of water is then admitted into the cavities 52 and 65 to coolthe faces of the cast to about 90° C. The upper plate of the press islifted, and the plate 63 lifts up the pins 80 which are retracted intothe counterform 61. Separation of the form 54 and counterform isachieved by means of the auxiliary jacks. The molded panel is removedand, if need be, placed on a conformator to bring it down to roomtemperature.

5. Finishing

The cooled panel is fettled. The washers 15 and braces 14 (FIG. 1 and 2)are glued on. Finally, layers of anti-erosion paint are applied.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:
 1. Apparatus for molding a perforated panel havingtubular protrusions surrounding the perforations on one side of eachpanel, said apparatus comprising:(a) a fixed mold part comprising:(i) afirst cooling plate assembly in which a water circulation cavity isformed; (ii) a molding form which rests on said first cooling plateassembly, said molding form having a plurality of cylindrical recessesin the working face thereof and through holes therethrough which areconcentric with said cylindrical recesses; and (iii) first means forassembling said first cooling plate assembly and said molding form and(b) a movable mold part comprising:(i) a second cooling plate assemblyin which a water circulation cavity is formed; (ii) a pin support plateresting on said second cooling plate assembly, a plurality of pins beingmounted in said pin support plate, said pins being sized, shaped, andpositioned so that, when the apparatus is in use, each one of said pinsextends through a corresponding one of said cylindrical recesses andinto a corresponding one of said through holes; (iii) a moldingcounterform which rests on said pin support plate; and (iv) second meansfor assembling said second cooling plate assembly and said pin supportplate, whereby, during use of the apparatus to mold a panel from aroughcast comprising a stack of precut layers of preimpregnated matcomprising glass felt having short fibers of glass held together byepoxy resin, said movable mold part is closed over said fixed mold partto define a molding cast therebetween and said plurality of pins passthrough the roughcast, pushing aside the glass fibers and forcing theminto said plurality of cylindrical recesses, after which said pins entersaid through holes, whereby a perforated panel having tubularprotrusions surrounding the perforations on one side of the panel isformed.
 2. Apparatus as recited in claim 1 and further including thirdmeans for moving said mold parts into a closed position before said pinspass through the roughcast.
 3. Apparatus as recited in claim 1 whereinpins are made of steel which has undergone a thermal oxidation treatmentin an atmosphere of humid argon, thereby forming an oxide layer on eachpin which favors adherence of an unmolding agent thereon.
 4. Apparatusas recited in claim 3 wherein said thermal oxidation treatment comprisedthe step of exposing said pins to an atmosphere of humid argon at thetemperature of 500° C. for four hours.